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Trait - is a form of a character Phenotype – what an organism looks like. Genotype – the specific alleles Alleles –forms of a gene Terminology

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Homozygous – a condition where an individual has two identical alleles (BB or bb) Heterozygous – a condition where the individual has two different alleles for the same gene (Bb)

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–Dominant Allele – the form of a gene that is expressed/visible in an organism (usually indicated with a capital letter, B) –Recessive Allele – the form of a gene that may be masked/unseen in an organism (usually indicated by a lower case letter, b) Terminology

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Albinism - a condition where the individual cannot make the pigment melanin. A=dominant, colored a = recessive, albino But if one A is present it will “override” the albinism a Recessive & Dominant Genes

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determined that for every trait, there must be two governing characters (factors), one from the sperm and one from the egg. Today, we call these “factors”, genes. Principles of dominance and segregation Gregor Mendel (1822-1884)

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All About Peas Mendel used pea plants when he studied the pattern of inheritance. Why peas?

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All About Peas –Peas are small, so large numbers can be kept in a reasonably small space. –Peas have a relatively short life cycle, so many generations could be studied in a short time.

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Since homozygous dominant and heterozygous individuals look the same, how do we know which is which? Test Cross – a cross with a homozygous recessive individual to check for the presence of a recessive allele in an individual with a dominant phenotype.

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Ex) White wool is desirable. Black wool is brittle and difficult to dye. Is a white ram homozygous(WW) or heterozygous(Ww) for white wool? (white = W, black = w) breed the ram with a black, homozygous recessive ewe. The results would be as follows:

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Incomplete Dominance – two equally dominant alleles produce a new phenotype that is a blend of the two forms, similar to blending colors in paint. Ex. If a red & a white snapdragon are crossed, the first generation of plants will be pink.

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Co-dominance – the interaction of two equally dominant alleles results in the expression of both genes at the same time. Ex. If a red shorthorn bull is crossed with the white cow, the calf will not be pink, but roan. The roan results from the intermixing of red and white hairs. =

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To clarify that a trait is incompletely dominant and not imply dominant or recessive, capital letters with superscripts are used to describe their combinations.

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many genes have more than two alternate forms many genes have more than two alternate forms Multiple Alleles

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Ex) Blood types are controlled by three different alleles: I A,I B and i. I A and I B alleles are co-dominant to each other, but both are dominant to i.I A and I B alleles are co-dominant to each other, but both are dominant to i. Multiple Alleles

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Di-Hybrid Crosses two pairs of genes considered simultaneouslytwo pairs of genes considered simultaneously

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Remember: The Law of Independent Assortment Genes on different chromosomes assort and segregate independently of one another during meiosis. The inheritance of one gene is unaffected by the inheritance of another.

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Probability Probability is the study of outcomes of events or occurrences. It can be expressed by the formula: Probability =# of chances for an event # of possible combinations

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Probability In genetics, we use probabilities to try to predict the likelihood of a specific trait showing up in the offspring. In determining the probability of an event, two important rules must be understood:

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Probability 1. The rule of independent events – states that chance has no memory, and sequential events are not linked.

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Probability 2. The product rule –multiply the chance of independent events. Ex) What is the chance of tossing three heads in a row? ½ x ½ x ½ = 1/8.

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Probability and Genetics What is the probability that a male and female both with genotype EeWw free earlobes and a widow’s peak will have a male child with a widows peak and free earlobes? What is the probability that a male and female both with genotype EeWw for free earlobes and a widow’s peak will have a male child with a widows peak and free earlobes?

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Pedigree Charts In humans, each generation might be 15 to 40 years apart. If a trait skips generations (is recessive), it may not appear for a much as 80 years before it is detected. A pedigree chart can be used to keep a visual record of the genetic characteristics in many generations of an organism.

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Pedigrees help determine inheritance patterns within individual families Pedigrees help determine inheritance patterns within individual families predict the probability that a couple will have a baby with a specific genetic disorder. predict the probability that a couple will have a baby with a specific genetic disorder.

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Assume that individuals III-2 and III-3 are expecting another child. Construct two Punnett squares to illustrate the two possible crosses, based on the mother’s (III-2) two possible genotypes. Calculate the probability of this child being a son with OTC deficiency. (Provide a legend to identify the symbols used for the two alleles.) (4 marks)